French

And most of all, brother, do not go buy bread.

“And above all, brother, do not go and buy bread.”

That is the closest rendering of Mallarmé’s “Et surtout ne va pas, frère, acheter du pain.” Your “most of all” is possible, but “above all” has greater finality and preserves the elevated, almost scriptural force of the closing line of “Alms.” The startling command is that the beggar must not reduce the gift to mere subsistence: do not turn the strange gold of poetry back into ordinary usefulness. Mallarmé’s “Aumône”⁠

Then why does it translate into buy bread? If everything depended on that last sentence, it would be totally overturned if it was rendered as buy bread instead of do not go buy bread.

You are right: rendering the full sentence as “buy bread” would completely overturn it. The French is unmistakably negative:

“Et surtout ne va pas, frère, acheter du pain.”

“Ne … pas” is the French negative construction. It surrounds “va,” the conjugated form of aller, and therefore negates the whole action “va acheter”: “go buy.” Without the negative—“Va, frère, acheter du pain”—it would mean “Go, brother, and buy bread.” With “ne va pas,” it means “Do not go buy bread,” or more idiomatically, “Do not, brother, go and buy bread.”

If a translator returns only “buy bread,” it is translating the isolated infinitive phrase “acheter du pain,” not Mallarmé’s complete sentence. The correct line cannot be affirmative. And because everything culminates in that prohibition, the strongest rendering is exactly:

“And above all, brother, do not go buy bread.”